Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$82.31	12.345%	$92.4712	$92.47	$92.45	$92.50
Purchase #2	$193.39	6.145%	$205.2738	$205.27	$205.25	$205.30
Purchase #3	$154.60	6.464%	$164.5933	$164.59	$164.60	$164.60
Purchase #4	$167.70	13.374%	$190.1282	$190.13	$190.15	$190.10
Purchase #5	$208.82	5.594%	$220.5014	$220.50	$220.50	$220.50
Purchase #6	$76.40	11.382%	$85.0958	$85.10	$85.10	$85.10
Purchase #7	$160.25	13.261%	$181.5008	$181.50	$181.50	$181.50
7 purchase totals =	$1,043.47		$1,139.5645	$1,139.56	$1,139.55	$1,139.60